1. Field of the Invention
The present invention is directed to an apparatus and method of depositing small-scale powders, and more particularly dispensing powders for a variety of applications including manufacturing small-scale devices such as micro-electromechanical systems (MEMS), biomedical instruments and display instruments.
2. Description of Related Art
Micro-electromechanical systems (MEMS) technology is a manufacturing technology that embodies a way of making complex electromechanical systems using batch fabrication techniques similar to the way integrated circuits are made, and making such electromechanical devices along with electronics. MEMS is used in a wide range of applications ranging from polymerized chain reaction (PCR) microsystems to blood pressure monitoring to air-bag accelerometers and active suspension systems for automobiles. Overall, MEMS is an enabling technology allowing the development of “smart” products by facilitating the computational ability of microelectronics in connection with the detection and control capabilities of small-scale sensors and small-scale actuators.
Classically, sensors and actuators have been the most costly and unreliable part of a macro-scale system which may include some combination of sensors, actuators and electronics. With a MEMS fabricated device, costs are typically significantly lower than a comparable macro scale system. Moreover, MEMS devices can be significantly more reliable than corresponding macro-scale systems. Note that the terms “micro-scale” and “macro-scale” are used herein to generically refer to small scale and large scale manufacturing techniques. The terms “micro” and “micro-scale” are not intended to limit the applicability of the present invention in any way.
In general, conventional MEMS manufacturing includes the integration of mechanical elements, sensors, actuators and electronics on, typically, a common silicon substrate through the use of micro fabrication technology. While the electronics are typically fabricated using integrated circuit (IC) process sequences (for example, CMOS), the micro-mechanical components are fabricated using compatible micro machining processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.
There are three basic building blocks in conventional MEMS fabrication technology including the ability to (1) deposit films of material on a substrate, (2) apply a patterned mask (application specific) on the films by photo lithographic imaging, and (3) etch the films selectively to the mask. With specific reference to the first of these, deposition can be accomplished, typically, via a chemical reaction (e.g., LPCVD, EPCVD, epitaxy, etc.) or a physical reaction (PVD including sputtering and evaporation). In general, CVD or chemical vapor deposition techniques (such as low CVD) produce superior films to physical vapor deposition techniques (PVD), but at the expense of higher material cost and higher process risk. In either case, the process equipment is complicated, expensive and typically requires clean-room conditions.
These MEMS techniques are two-dimensional (2D) processes with multiple steps that require complicated processing procedures, and only a limited number of materials can be processed through the use of these techniques. And, as 2D processes, these silicon-based techniques are not easily adaptable to building 3D devices such that enclosed volumes of arbitrary shape and composition are difficult to make without the use of micro assembly.
Overall, although the most widely used MEMS fabrication material, there are significant drawbacks associated with fabricating MEMS devices with silicon. Conventional methods of fabricating silicon-based devices have a litany of limitations including the types of devices that can be produced, as well as strict process conditions. In addition, silicon itself has several shortcomings as a structural/mechanical material.
In addition, the reliable mechanical properties of MEMS are critical to the safety and functioning of these complex devices. In this regard, MEMS should be capable of being built using a wider selection of materials, including alloys, polymers, ceramics and heterogeneous materials that have superior mechanical and thermal properties to silicon. Micro-components with high aspect ratios, complex geometries, three-dimensional and complex microstructures are essential in many applications and can deliver a new generation of functionality and performance. Nevertheless, little work has been done to successfully attain efficient micro-manufacturing techniques for the fabrication of functionally and geometrically complex heterogeneous MEMS.
A significant challenge to the proliferation of MEMS devices is the development of processes that can be implemented in the wide range of applications and materials. Many of the largest beneficiaries of MEMS technology will be firms that have no capability or competency in micro fabrication technology. As a result, a manufacturing solution allowing these organizations to have responsive and affordable access to MEMS fabrication resources for prototyping and manufacturing is desired.
Another technology evolving concurrently with MEMS development, known as solid freeform fabrication (SFF) (also called “layered manufacturing” or “rapid prototyping”) has emerged as a popular manufacturing technology for rapid production. SFF machines build parts layer-by-layer directly from CAD models without the fixturing/tooling or human intervention demanded of conventional processes. This manufacturing technology enables the building of parts that have traditionally been impossible to fabricate because of their complex shapes or of their variety of materials. A variety of SFF processes have been used to create multi-material parts.
Referring to FIG. 1, an SFF system 10 includes a first CPU 12 having CAD/CAM software to communicate a particular design of a device to be fabricated to the process components of system 10. In particular, CPU 12 communicates with an automatic process planner 14 which, typically, slices the CAD data from CPU 12 to a two-dimensional layer. Further, process planner 14 provides trajectory planning, as known in the field. Process planner 14 thereafter communicates with a process machine 16 to provide motion control for automatic layered fabrication of the device.
Known SFF techniques include 3D printing that has been applied to build parts with composition control. Other SFF processes include SLS (selective laser sintering) that has been used to build multi-material and functionally gradient materials, and LENS (laser engineered net shape) which has been used to tailor certain physical properties of materials.
In addition, research in this area has been directed to using several layered manufacturing processes to create 3D micro-scale components. For instance, micro-stereo lithography has been used to develop complex 3D microstructures. Movable microstructures have been made by the use of two-photon 3D micro-fabrication with sub micron resolution and electrochemical fabrication (EFAB) is a technique that specializes in the fabrication of dense micro-metal parts by electroplating. Although useful for their particular purposes, each of these micro SFF processes are not suitable to build 3D heterogeneous MEMS due to their limited flexibility in changing material composition in situ.
Another emerging SFF process, known as laser-assisted shape deposition manufacturing (SDM), has been developed to fabricate macro-scale fully dense structures. In comparison to most additive SFF processes, SDM uses sequential additive (deposition of part materials and sacrificial materials) and subtractive (material removal) steps to form 3D structures, similar to traditional techniques.
Notably, SDM allows control of material location and material properties in 3D space. SDM has been used to build complex 3D macro-shapes with internal cooling channels, parts with continuously varying material properties, mechanisms, and heterogeneous parts with embedded sensors and actuators. However, SDM processes have not been scaled down to the small-scale, e.g., micro-world. For such an evolution, it was essential that the tools be capable of realizing additive and subtractive processes at the micro-scale.
Lasers, as versatile tools, have been used for heating, melting, and ablation. One laser-based tool, known as laser micro-machining, relies on the process of ablation. Laser micro-machining, especially with an excimer laser, can be used on a wide range of materials including polymers, ceramics, semi-conductors and metals.
While laser micro-machining is a subtractive process, laser micro deposition is an additive process. Laser particulate guidance (LPG) has been used to deposit materials at a 10 micron line width.
Because of its ability to produce a small laser spot size, micro-scale laser materials processing has become popular for micro-fabrication. Laser micro-machining processes create 2D and 3D MEMS in a spectrum of homogeneous materials. Nevertheless, known laser micro deposition processes are not capable of in situ local composition control of the material being deposited. Importantly, this composition control is vital to the production of heterogeneous micro-structures. The primary drawback with known systems is the inability to mix and deliver various submicron/nano dry powders without additional chemical mixtures.
In view of the above-stated needs, the field of MEMS technology was in need of an improved manufacturing process allowing the fabrication of three-dimensional MEMS devices with a wide range of materials. The desired apparatus and method would provide an effective method of delivering small-scale dry powders to a substrate so as to maintain in situ local deposition control, and would also facilitate heterogeneous materials processing. Such a system would afford advantages in terms of no contact with the substrate during process, no chemicals, flexible feature size and shape, high precision, and the ability to work in air and at room temperature so as to obviate the above-noted problems with conventional MEMS techniques.